My aim is to determine the behavioral role(s) of the brain peptides bombesin (BBS) and cholecystokinin (CCK), especially their possible roles in satiety and satiety-related behaviors. This aim has developed from conclusions from experiments I carried out during the previous award period. Experiments using rats and rhesus monkeys showed: (1) Food stimulation of the pregastric gut surface is not sufficient to produce normal satiety. (2) Food stimulation to the pregastric and gastric gut surfaces is sufficient to end a meal and elicit the typical behaviors of satiety; therefore, a potent satiety signal originates at the gastric level. (3) Food stimulation fo the pregastric and intestinal gut surfaces is sufficient to end a meal and elicit the typical behaviors of satiety; therefore, a potent satiety signal originates at the intestinal level. This intestinal signal can operate in the absence of gastric distention. (4) Peripherally-administered CCK (a hormone released from intestine by food) has a potent, dose-related satiety action which can operate in the absence of gastric distention; this satiety action of CCK has also been demonstrated in three human studies. (5) Peripherally-administered BBS (a peptide released from stomach and/or intestine by food) also has a potent, dose related satiety action. BBS-like and CCK-like peptides are located in brain neurons in very high concentrations. This finding, together with my conclusions listed above, suggest behavioral roles for these peptides, possibly related to satiety. I therefore plan to administer BBS, CCK, their analogues and antagonists directly into brain sites known to contain high concentrations of these peptides and their receptors, and to examine the behavioral effects of these manipulations; special attention will be directed toward effects on satiety and the behaviors closely associated with satiety. This research has practical implications for the treatment of obesity and diseases complicated by obesity, and it has fundamental implications for the study of behavior.